Golf ball

ABSTRACT

A golf ball which has excellent abrasion-resistance and spin performance is provided. The golf ball of the present invention includes a core and a cover covering the core and containing polyurethane as a resin component, wherein the polyurethane has, as a constituting component, a polyisocyanate component, a high-molecular weight polyol component, and a mixture of cis-1,4-cyclohexane dimethanol and trans-1,4-cyclohexane dimethanol as a chain extender.

FIELD OF THE INVENTION

The present invention relates to a technology for improving a cover,especially a technology for improving a urethane cover.

DESCRIPTION OF THE RELATED ART

As a resin component constituting a cover of a golf ball, an ionomerresin or polyurethane is used. Covers containing an ionomer resin arewidely used for their excellent repulsion, durability andprocessability. However, the problems have been pointed out that theshot feeling is poor because of the high rigidity and hardness and thatthe controllability is also poor because of the insufficient spinperformance. On the other hand, if polyurethane is used as the resincomponent, it is known that the shot feeling and spin performance areimproved compared with an ionomer resin.

JP2005-523958T discloses a golf ball comprising a core and a cover, thecover comprising a polyurethane elastomer, the polyurethane elastomercomprising the reaction product of (a) a HDI-terminated prepolymercomprising the reaction product of one or more polyols with astoichiometric excess of HDI diisocyanate monomer wherein unreacted HDIdiisocyanate monomer is removed to less than about 2 wt. % and (b) atleast one hydroxy or amine functional chain extender.

JP2008-195955A discloses a golf ball comprising a core and a cover, thecover comprising a polyurethane elastomer, the polyurethane elastomercomprising the reaction product of (a) a HDI-terminated prepolymercomprising the reaction product of one or more polyols selected from thegroup consisting of polyesters, polycaprolactones, polyethers,polycarbonates, and hydrocabon polyols with a stoichiometric excess ofHDI diisocyanate monomer and prepared without using a solvent whereinunreacted HDI diisocyanate monomer is removed to less than about 2 wt. %and (b) at least one hydroxy or amine functional chain extender.

JP2007-90065A discloses a golf ball comprising a core and one more coverlayer which encloses the core, the ball being characterized in that atleast one cover layer is made primarily of a thermoplastic polyurethaneelastomer obtained by a curing reaction of an original polyurethaneliquid containing a polyol component and a polyisocyanate component,wherein the polyol component includes a copolymeric polycarbonatepolyol.

JP2005-28153A discloses a multilayer golf ball formed, at least in part,from a polyurethane or polyurea composition. The polyurethane orpolyurea composition may include at least one diisocyanate, at least onepolyol(polyurethane) or amine-terminated moiety(polyurea), and at leastone curing agent.

SUMMARY OF THE INVENTION

In general, golf balls having a soft cover are excellent in the spinperformance, but the abrasion-resistance is poor, while golf ballshaving a hard cover are excellent in the abrasion-resistance, but thespin performance is poor. That is, the spin performance and theabrasion-resistance are contradictory properties, and it is required tostrike a balance between the spin performance and theabrasion-resistance. The present invention has been made in view of theabove circumstances, and an object of the present invention is toprovide a golf ball having an excellent abrasion-resistance and spinperformance in a golf ball using a polyurethane cover.

The present invention which has solved the above problems provides agolf ball comprising: a core; and a cover covering the core andcontaining polyurethane as a resin component, wherein the polyurethanehas, as a constituting component, a polyisocyanate component, ahigh-molecular weight polyol component, and a mixture ofcis-1,4-cyclohexane dimethanol and trans-1,4-cyclohexane dimethanol as achain extender. As a result of the aggressive research by the presentinventors, the present inventors have achieved the present inventionbased on the finding that the use of a mixture of cis-1,4-cyclohexanedimethanol and trans-1,4-cyclohexane dimethanol as a chain extenderprovides the golf ball with the abrasion-resistance and spin performancewhich are well-balanced. The mixing ratio (cis/trans) ofcis-1,4-cyclohexane dimethanol and trans-1,4-cyclohexane dimethanolpreferably ranges from 10/90 to 70/30 in a mass ratio. If the mixingratio falls within the above range, it is possible to strike a balancebetween the abrasion-resistance and the spin performance at the higherlevel.

The present invention provides a golf ball which has the excellentabrasion-resistance and spin performance in a golf ball with a coverusing a polyurethane as a resin component.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to a golf ball comprising: a core; anda cover covering the core and containing polyurethane as a resincomponent, wherein the polyurethane has, as a constituting component, apolyisocyanate component, a high-molecular weight polyol component, anda mixture of cis-1,4-cyclohexane dimethanol and trans-1,4-cyclohexanedimethanol (hereinafter, sometimes may be referred to as “cis-transmixture”) as a chain extender.

First, the polyurethane used in the present invention will be explained.The polyurethane is not limited, as long as the polyurethane is obtainedby a reaction of polyisocyanate, the high-molecular weight polyol, andthe cis-trans mixture as a chain extender, which are constitutingcomponents. The polyurethane may be a thermoplastic polyurethane or athermosetting polyurethane. In the following, each of the componentswill be explained.

In the present invention, the mixture of cis-1,4-cyclohexane dimethanoland trans-1,4-cyclohexane dimethanol is used as the chain extender. Thebalance between the abrasion-resistance and the spin performance can bestruck by using the mixture of cis-compound and trans-compound.

The mixing ratio (cis/trans) is preferably 70/30 or less, morepreferably 60/40 or less, even more preferably 50/50 or less, and ispreferably 10/90 or more, more preferably 20/80 or more, even morepreferably 30/70 or more, in a mass ratio. If the mixing ratio fallswithin the above range, the balance between the abrasion-resistance andthe spin performance can be struck at the higher level.

The cis-trans mixture can be obtained by mixing 1,4-cyclohexanedimethanol (a mixture of cis-compound and trans-compound, cis content:74 mass %) and trans-1,4-cyclohexane dimethanol (trans content: 100 mass%), available from TOKYO CHEMICAL INDUSTRY Co., Ltd, in a desired mixingratio.

Although the polyurethane used in the present invention preferablycontains only the cis-trans mixture of cyclohexane dimethanol as a chainextender, other chain extenders may be used as a constituting componentto the extent that the effect of the present invention is not impaired.Other chain extenders include a low-molecular weight polyol or alow-molecular weight polyamine. Examples of the low-molecular weightpolyol may include a diol such as ethylene glycol, diethylene glycol,triethylene glycol, propanediol (e.g., 1,2-propanediol, 1,3-propanediol,and 2-methyl-1,3-propanediol), dipropylene glycol, butanediol (e.g.,1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, and2,3-dimethyl-2,3-butanediol), neopentyl glycol, pentanediol, hexanediol,heptanediol, octanediol, an aniline diol, and a bisphenol A diol; atriol such as glycerin, trimethylol propane, and hexanetriol; a tetraolor a hexanol such as pentaerythritol and sorbitol.

The low-molecular weight polyamine that can be used as a chain extendermay include any polyamine, as long as it has at least two amino groups.The polyamine includes an aliphatic polyamine such as ethylenediamine,propylenediamine, butylenediamine, and hexamethylenediamine, analicyclic polyamine such as isophoronediamine, piperazine, and anaromatic polyamine.

The aromatic polyamine has no limitation as long as it has at least twoamino groups directly or indirectly bonded to an aromatic ring. Herein,the “indirectly bonded to the aromatic ring”, for example, means thatthe amino group is bonded to the aromatic ring via a lower alkylenebond. Further, the aromatic polyamine includes, for example, amonocyclic aromatic polyamine having at least two amino groups bonded toone aromatic ring or a polycyclic aromatic polyamine having at least twoaminophenyl groups each having at least one amino group bonded to onearomatic ring.

Examples of the monocyclic aromatic polyamine include a type such asphenylenediamine, tolylenediamine, diethyltoluenediamine, anddimethylthiotoluenediamine wherein amino groups are directly bonded toan aromatic ring; and a type such as xylylenediamine wherein aminogroups are bonded to an aromatic ring via a lower alkylene group.Further, the polycyclic aromatic polyamine may include apoly(aminobenzene) having at least two aminophenyl groups directlybonded to each other or a compound having at least two aminophenylgroups bonded via a lower alkylene group or an alkylene oxide group.Among them, a diaminodiphenylalkane having two aminophenyl groups bondedto each other via a lower alkylene group is preferable. Typicallypreferred are 4,4′-diaminodiphenylmethane or the derivatives thereof.The other chain extender preferably has a molecular weight of 400 orless, more preferably 350 or less, even more preferably 300 or less andpreferably has a molecular weight of 30 or more, more preferably 40 ormore, even more preferably 45 or more. If the molecular weight is toolarge, it is difficult to distinguish the chain extender from thehigh-molecular weight polyol constituting a soft segment of thepolyurethane.

The polyisocyanate component constituting the polyurethane used in thepresent invention is not limited, as long as it has at least twoisocyanate groups. Examples of the polyisocyanate include an aromaticpolyisocyanate such as 2,4-tolylene diisocyanate, 2,6-tolylenediisocyanate, a mixture of 2,4-tolylene diisocyanate and 2,6-tolylenediisocyanate (TDI), 4,4′-diphenylmethane diisocyanate (MDI),1,5-naphthylene diisocyanate (NDI), 3,3′-bitolylene-4,4′-diisocyanate(TODI), xylylene diisocyanate (XDI), tetramethylxylylenediisocyanate(TMXDI), para-phenylene diisocyanate (PPDI); an alicyclic polyisocyanateor aliphatic polyisocyanate such as 4,4′-dicyclohexylmethanediisocyanate (H₁₂MDI), hydrogenated xylylenediisocyanate (H₆XDI),hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), andnorbornene diisocyanate (NBDI). These may be used either alone or as amixture of at least two of them.

In view of improving the abrasion-resistance, the aromaticpolyisocyanate is preferably used as the polyisocyanate component of thepolyurethane. Use of the aromatic polyisocyanate improves the mechanicalproperty of the obtained polyurethane and provides the cover with theexcellent abrasion-resistance. In addition, in view of improving theweather resistance, as the polyisocyanate component of the polyurethane,a non-yellowing type polyisocyanate such as TMXDI, XDI, HDI, H₆XDI,IPDI, H₁₂MDI and NBDI is preferably used. More preferably,4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) is used. Since4,4′-dicyclohexylmethane diisocyanate (H₁₂MDI) has a rigid structure,the mechanical property of the resulting polyurethane is improved, andthus the cover which is excellent in abrasion-resistance can beobtained.

The high-molecular polyol component constituting the polyurethane is notlimited, as long as it has a plurality of hydroxyl groups. Such examplesof the high-molecular weight polyol include a polyether polyol such aspolyoxyethylene glycol (PEG), polyoxypropylene glycol (PPG), andpolyoxytetramethylene glycol (PTMG); a condensed polyester polyol suchas polyethylene adipate (PEA), polybutylene adipate (PBA), andpolyhexamethylene adipate (PHMA); a lactone polyester polyol such aspoly-ε-caprolactone (PCL); a polycarbonate polyol such aspolyhexamethylene carbonate; and an acrylic polyol. The above polyolsmay be used alone or as a mixture of at least two of them. Among them,as a high-molecular weight polyol, a high molecular weight diol ispreferably used.

A number average molecular weight of the high-molecular weight polyol isnot particularly limited, and for example, it is preferably more than400, more preferably 800 or more, even more preferably 1,000 or more. Ifthe number average molecular weight of the high-molecular weight polyolis too small, the resultant polyurethane becomes too hard and the shotfeeling of the golf ball is lowered. The upper limit of the numberaverage molecular weight of the high-molecular weight polyol is notparticularly limited, and it is preferably 10,000, more preferably8,000. The number average molecular weight of the polyol component canbe measured by Gel permeation Chromatography using two columns ofTSK-GEL SUPREH 2500 (TOSOH Corporation) as a column, polystyrene as astandard material, and tetrahydrofuran as an eluate.

The high-molecular weight polyol preferably has a hydroxyl value of 500mgKOH/g or less, more preferably 250 mgKOH/g or less, even morepreferably 100 mgKOH/g or less. The hydroxyl value of the high-molecularweight polyol can be measured for example, by an acetylation methodaccording to JIS K₁₅₅₇-1.

The polyurethane preferably has a slab hardness of 15 or more, morepreferably 20 or more, and preferably has a slab hardness of 50 or less,more preferably 45 or less, even more preferably 42 or less in Shore Dhardness. If the slab hardness is too low, the spin rate may increase onthe driver shot, while if the slab hardness is too high, the spin ratemay decrease on the approach shot.

The polyurethane has no limitation on the constitutional embodimentsthereof. Examples of the constitutional embodiments are the embodimentwhere the polyurethane consists of the polyisocyanate component, thehigh-molecular weight polyol component and the cis-trans mixture as thechain extender; and the embodiment where the polyurethane consists ofthe polyisocyanate component, the high-molecular weight polyolcomponent, the cis-trans mixture and other chain extenders as the chainextender.

The polyurethane may be either thermoplastic polyurethane orthermosetting polyurethane. The thermoplastic polyurethane ispolyurethane exhibiting plasticity by heating and generally meanspolyurethane having a straight chain structure of a high molecularweight to a certain extent. On the other hand, the thermosettingpolyurethane (two-component curing type polyurethane) is polyurethaneobtained by temporarily preserving a low-molecular weight urethaneprepolymer, and reacting the prepolymer with a chain extender (curingagent) to increase a molecular weight thereof immediately before moldingthe cover. The thermosetting polyurethane includes polyurethane having astraight chain structure or polyurethane having a three-dimensionalcrosslinked structure depending on a number of a functional group of theprepolymer or the chain extender (curing agent) to be used. In thepresent invention, the thermoplastic polyurethane is preferable.

Examples of a method for synthesizing the polyurethane include aone-shot method and a prepolymer method. The one-shot method is a methodof reacting a polyisocyanate component, a polyol component or the likeat once. The prepolymer method is a method of reacting a polyisocyanatecomponent and a polyol component or the like in multiple steps. Forexample, a low-molecular-weight urethane prepolymer is synthesized, andsubsequently the urethane prepolymer is polymerized to have ahigh-molecular weight. The polyurethane used in the present invention ispreferably produced by the prepolymer method.

As an example of producing the polyurethane by the prepolymer method,the following case will be described in detail, wherein an isocyanategroup terminated urethane prepolymer is synthesized and then polymerizedwith the cis-trans mixture as the chain extender.

First, a polyisocyanate component is subjected to a urethane reactionwith a high-molecular weight polyol component to synthesize anisocyanate group terminated urethane prepolymer. In this case, thecharging ratio of the polyisocyanate component to the high-molecularweight polyol component is, preferably 1 or larger, more preferably 1.2or larger, and even more preferably 1.5 or larger, and is preferably 10or smaller, more preferably 9 or smaller, and even more preferably 8 orsmaller in a molar ratio (NCO/OH) of the isocyanate group (NCO)contained in the polyisocyanate component to the hydroxyl group (OH)contained in the polyol component.

The temperature at which the prepolymer reaction is performed ispreferably 10° C. or higher, more preferably 30° C. or higher, and evenmore preferably 50° C. or higher, and is preferably 200° C. or lower,more preferably 150° C. or lower, and even more preferably 100° C. orlower. The reaction time for the prepolymer reaction is preferably 10minutes or longer, more preferably 1 hour or longer, and even morepreferably 3 hours or longer, and is preferably 32 hours or shorter,more preferably 16 hours or shorter, and even more preferably 8 hours orshorter.

Next, the obtained isocyanate group terminated urethane prepolymer issubjected to a chain extension reaction with the cis-trans mixture as achain extender component to obtain the polyurethane. In this case, thecharging ratio of the isocyanate group terminated urethane prepolymer tothe chain extender component is preferably 0.9 or larger, morepreferably 0.92 or larger, and even more preferably 0.95 or larger, andis preferably 1.1 or smaller, more preferably 1.08 or smaller, and evenmore preferably 1.05 or smaller in a molar ratio (NCO/OH) of theisocyanate group (NCO) contained in the isocyanate group terminatedurethane prepolymer to the hydroxyl group (OH) contained in the chainextender component.

The temperature at which the chain extension reaction is performed ispreferably 10° C. or higher, more preferably 30° C. or higher, and evenmore preferably 50° C. or higher, and preferably 220° C. or lower, morepreferably 170° C. or lower, and even more preferably 120° C. or lower.The reaction time for the chain extension reaction is preferably 10minutes or longer, more preferably 30 minutes or longer, and even morepreferably 1 hour or longer, and preferably 20 days or shorter, morepreferably 10 days or shorter, and even more preferably 5 days orshorter.

Both of the prepolymer reaction and the chain extension reaction arepreferably conducted in an atmosphere of nitrogen.

In synthesizing the polyurethane, a known catalyst may be used as longas it does not impair the effect of the present invention. Examples ofthe catalyst include a monoamine such as triethylamine, andN,N-dimethylcyclohexylamine; a polyamine such asN,N,N′,N′-tetramethylethylenediamine, andN,N,N′,N″,N″-pentamethyldiethylenetriamine; a cyclic diamine such as1,8-diazabicyclo-[5.4.0]-7-undecene (DBU), triethylenediamine; atin-based catalyst such as dibutyl tin dilaurylate, and dibutyl tindiacetate. Each of these catalysts may be used solely, or two or more ofthese catalysts may be used in combination. Among these catalysts, atin-based catalyst such as dibutyl tin dilaurylate, and dibutyl tindiacetate are preferable, and in particular, dibutyl tin dilaurylate ispreferably used.

A mass ratio (cis/trans) of the cis-structure molecule to the transstructure molecule in 1,4-cyclohexane dimethanol constituting thesynthesized polyurethane can be measured as follows. The polyurethane issubjected to a treatment with a DMF solution containing n-butylamine ora heat treatment to break urethane bonds in the polyurethane, and theresulting material is analyzed by gas chromatography, or other similarmethods.

A concentration of n-butylamine in the DMF solution preferably rangesfrom 0.01 mol/l to 0.25 mol/l, and is more preferably 0.05 mol/l. Theheat treatment is preferably performed, for example, at a temperatureranging from 130° C. to 150° C. for a time period ranging from 2 hoursto 4 hours.

The cover of the present invention may contain other resin components inaddition to the polyurethane as a resin component, as long as it doesnot impair the effect of the present invention. Examples of the otherresin component include an ionomer resin, a thermoplastic elastomer, adiene block copolymer, or the like.

Examples of the ionomer resin include one prepared by neutralizing atleast a part of carboxyl groups in a copolymer, composed of ethylene andαβ-unsaturated carboxylic acid having a carbon number of 3 to 8 with ametal ion; one prepared by neutralizing at least a part of carboxylgroups in a terpolymer composed of ethylene, αβ-unsaturated carboxylicacid having a carbon number of 3 to 8, and αβ-unsaturated carboxylicacid ester with a metal ion; or a mixture of these two. Examples of theαβ-unsaturated carboxylic acid include acrylic acid, methacrylic acid,fumaric acid, maleic acid, crotonic acid, or the like. In particular,acrylic acid and methacrylic acid are preferable. Examples of theαβ-unsaturated carboxylic acid ester include methyl ester, ethyl ester,propyl ester, n-butyl ester, isobutyl ester of acrylic acid, methacrylicacid, fumaric acid, and maleic acid. In particular, acrylic acid esterand methacrylic acid ester are preferable. Examples of the metal ion forneutralizing at least a part of the carboxyl groups in the copolymercomposed of ethylene and the αβ-unsaturated carboxylic acid or in theterpolymer composed of ethylene, the αβ-unsaturated carboxylic acid, andthe αβ-unsaturated carboxylic acid ester are; monovalent metal ions suchas sodium, potassium, and lithium; divalent metal ions such asmagnesium, calcium, zinc, barium, and cadmium; trivalent metal ions suchas aluminum, or other metal ions such as tin and zirconium. Inparticular, sodium ion, zinc ion, and magnesium ion are preferably usedin view of the resilience and durability of the golf ball.

Specific examples of the ionomer resin include “Himilan (registeredtrade mark)” available from MITSUI-DUPONT POLYCHEMICAL CO., LTD, “Surlyn(registered trade mark)” available from DUPONT CO, and “Iotek(registeredtrade mark)” available from Exxon Co.

Specific examples of the thermoplastic elastomer includes athermoplastic polyamide elastomer having a commercial name of “PEBAX”,for example, “PEBAX 2533”, available from ARKEMA Inc; a thermoplasticpolyester elastomer having a commercial name of “HYTREL”, for example,“HYTREL 3548” and “HYTREL 4047” available from DU PONT-TORAY Co.; and athermoplastic polystyrene elastomer having a commercial name of“RabaIon” available from Mitsubishi Chemical Co. Among them, thethermoplastic polystyrene elastomer is preferable. The thermoplasticpolystyrene elastomer includes, for example, a polystyrene-diene blockcopolymer comprising a polystyrene block component as a hard segment anda diene block component, for example polybutadiene, isoprene,hydrogenated polybutadiene, hydrogenated polyisoprene, as a softsegment. The polystyrene-diene block copolymer comprises a double bondderived from a conjugated diene compound of block copolymer or partiallyhydrogenated block copolymer. Examples of the polystyrene-diene blockcopolymer are a block copolymer having a SBS (styrene-butadiene-styrene)comprising polybutadiene block; and a block copolymer having a SIS(styrene-isoprene-styrene) structure.

In the case that another resin component is used as the resin componentfor the cover of the present invention in addition the polyurethane, theresin component preferably contains the polyurethane as the maincomponent. The resin component preferably contains the polyurethane inan amount of 50 mass % or higher, more preferably 60 mass % or higher,and even more preferably 70 mass % or higher. Further, it is alsopreferable that the resin component essentially consists of thepolyurethane.

The cover of the golf ball of the present invention may contain apigment component such as a white pigment (titanium oxide) and a bluepigment, a gravity adjusting agent such as calcium carbonate and bariumsulfate, a dispersant, an antioxidant, an ultraviolet absorber, a lightstabilizer, a fluorescent material or a fluorescent brightener, as longas the cover performance is not damaged.

The content of the white pigment (titanium oxide) is preferably 0.5 partby mass or more, more preferably 1 part by mass or more, and preferably10 parts by mass or less, more preferably 8 parts by mass or less basedon 100 parts by mass of the resin component constituting the cover. Thewhite pigment in an amount of 0.5 part by mass or more can impartopacity to the cover, while the white pigment in an amount of more than10 parts by mass may lower the durability of the resulting cover.

An embodiment for molding a cover is not particularly limited, andincludes an embodiment which comprises injection molding the covercomposition directly onto the core, or an embodiment which comprisesmolding the cover composition into a hollow-shell, covering the corewith a plurality of the hollow-shells and subjecting the core with aplurality of the hollow shells to the compression-molding (preferably anembodiment which comprises molding the cover composition into a halfhollow-shell, covering the core with the two half hollow-shells, andsubjecting the core with the two half hollow-shells to thecompression-molding). In the case of directly injection molding thecover composition onto the core, it is preferred to use upper and lowermolds for forming a cover having a spherical cavity and pimples, whereina part of the pimple also serves as a retractable hold pin. When formingthe cover by injection molding, the hold pin is protruded to hold thecore, and the cover composition which has been heated and melted ischarged and then cooled to obtain a cover. For example, the covercomposition heated and melted at the temperature of 150° C. to 230° C.is charged into a mold held under the pressure of 980 KPa to 1,500 KPafor 0.1 to 1 second. After cooling for 15 to 60 seconds, the mold isopened and the golf ball with the cover molded is taken out from themold.

Molding of the half shell can be performed by either compression moldingmethod or injection molding method, and the compression molding methodis preferred. The compression-molding of the cover composition into halfshell can be carried out, for example, under a pressure of 1 MPa or moreand 20 MPa or less at a temperature of −20° C. or more and 70° C. orless relative to the flow beginning temperature of the covercomposition. By performing the molding under the above conditions, ahalf shell having a uniform thickness can be formed. Examples of amethod for molding the cover using half shells include compressionmolding by covering the core with two half shells. The compressionmolding of half shells into the cover can be carried out, for example,under a pressure of 0.5 MPa or more and 25 MPa or less at a temperatureof −20° C. or more and 70° C. or less relative to the flow beginningtemperature of the cover composition. By performing the molding underthe above conditions, a cover for a golf ball having a uniform thicknesscan be formed.

When molding a cover, the concave portions called “dimple” are usuallyformed on the surface. After the cover is molded, the mold is opened andthe golf ball body is taken out from the mold, and as necessary, thegolf ball body is preferably subjected to surface treatment such asdeburring, cleaning, and sandblast. If desired, a paint film or a markmay be formed.

The thickness of the cover of the golf ball of the present invention isnot particularly limited; however, it is preferably 0.3 mm or more, morepreferably 0.5 mm or more, and even more preferably 0.7 mm or more. Ifthe thickness of the cover is too thin, the abrasion-resistance may belowered. Also, the thickness of the cover is preferably 2.5 mm or less,more preferably 2.3 mm or less, and even more preferably 2.1 mm or less.If the thickness of the cover is too thick, the repulsion property maybe lowered.

The cover composition preferably has the slab hardness of 20 or more,more preferably 22 or more, and even more preferably 24 or more, andpreferably has the slab hardness of 50 or less, more preferably 48 orless in Shore D hardness. If the slab hardness of the cover is less than20, the repulsion property of the golf ball may be lowered, resulting inshortening a flight distance, while if the cover hardness is more than50, the durability of the obtained golf ball may be lowered. The slabhardness of the cover can be measured by molding the cover compositioninto a sheet with a thickness of about 2 mm by hot press molding,preserving the sheet at 23° C. for 2 weeks, stacking three or more ofthe preserved sheet on one another to avoid being affected by themeasuring substrate on which the sheets are placed and carrying out themeasurement of the stack by a Shore D type spring hardness testerprescribed by ASTM-D2240.

Next, a preferred embodiment of the core of the golf ball of the presentinvention will be explained. The core of the golf ball of the presentinvention includes a single-layered core, a core consisting of a centerand a single-layered intermediate layer covering the core, a coreconsisting of a center and multi-piece or multi-layer of intermediatelayers covering the center. The core preferably has a spherical shape.If the core does not have a spherical shape, the cover does not have auniform thickness. As a result, there exist some portions where theperformance of the cover is lowered. On the other hand, the centergenerally has the spherical shape, but the center may be provided with arib on the surface thereof so that the surface of the spherical centeris divided by the ribs, preferably the surface of the spherical centeris evenly divided by the ribs. In one embodiment, the ribs arepreferably formed on the surface of the spherical center in anintegrated manner, and in another embodiment, the ribs are formed as anintermediate layer on the surface of the spherical center.

The ribs are preferably formed along an equatorial line and meridiansthat evenly divide the surface of the spherical center, if the sphericalcenter is assumed as the earth. For example, if the surface of thespherical center is evenly divided into 8, the ribs are formed along theequatorial line, any meridian as a standard, and meridians at thelongitude 90 degrees east, longitude 90 degrees west, and the longitude180 degrees east(west), assuming that the meridian as the standard is atlongitude 0 degree. If the ribs are formed, the depressed portiondivided by the ribs are preferably filled with a plurality ofintermediate layers or with a single-layered intermediate layer thatfills each of the depressed portions to make a core in the sphericalshape. The shape of the ribs, without limitation, includes an arc or analmost arc (for example, a part of the arc is removed to obtain a flatsurface at the cross or orthogonal portions thereof).

The core or the center of the golf ball of the present invention, ispreferably molded into a spherical shape by, for example, heat-pressinga rubber composition (hereinafter, simply referred to as “core rubbercomposition” in some cases) containing a base rubber, a crosslinkinginitiator, a co-crosslinking agent, and where necessary a filler.

As the base rubber, a natural rubber or a synthetic rubber can be used.Such examples include a polybutadiene rubber, a natural rubber, apolyisoprene rubber, a styrene polybutadiene rubber, andethylene-propylene-diene terpolymer (EPDM). Among them, typicallypreferred is the high cis-polybutadiene having cis-1,4 bond in aproportion of 40% or more, more preferably 70% or more, even morepreferably 90% or more in view of its superior repulsion property. Thecrosslinking initiator is blended to crosslink the base rubbercomponent.

As the crosslinking initiator, an organic peroxide is preferably used.Examples of the organic peroxide for use in the present invention aredicumyl peroxide, 1,1-bis(t-butylperoxy)-3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy)hexane, and di-t-butyl peroxide. Amongthem, dicumyl peroxide is preferable. An amount of the crosslinkinginitiator to be blended in the rubber composition is preferably 0.2 partby mass or more, more preferably 0.3 part by mass or more, and ispreferably 3 parts by mass or less, more preferably 2 parts by mass orless based on 100 parts by mass of the base rubber. If the amount isless than 0.2 part by mass, the core becomes too soft, and theresilience tends to be lowered, and if the amount is more than 3 partsby mass, the amount of the co-crosslinking agent needs to be increasedin order to obtain an appropriate hardness, which may cause theinsufficient resilience.

The co-crosslinking agent is not particularly limited, as long as it hasthe effect of crosslinking a rubber molecule by graft polymerization toa base rubber molecular chain; for example, αβ-unsaturated carboxylicacid having 3 to 8 carbon atoms or a metal salt thereof, more preferablyacrylic acid, methacrylic acid or a metal salt thereof may be used. Asthe metal constituting the metal salt, for example, zinc, magnesium,calcium, aluminum and sodium may be used, and among them, zinc ispreferred because it provides high resilience. The amount of theco-crosslinking agent to be used is preferably 10 parts or more, morepreferably 20 parts or more, and is preferably 50 parts or less, morepreferably 40 parts or less based on 100 parts of the base rubber bymass. If the amount of the co-crosslinking agent to be used is less than10 parts by mass, the amount of the organic peroxide must be increasedto obtain an appropriate hardness which tends to lower the resilience.On the other hand, if the amount of the co-crosslinking agent to be usedis more than 50 parts by mass, the core becomes too hard, so that theshot feeling may be lowered.

The filler contained in the core rubber composition is mainly blended asa gravity adjusting agent in order to adjust the specific gravity of thegolf ball obtained as the final product in the range of 1.0 to 1.5, andmay be blended as required. Examples of the filler include an inorganicfiller such as zinc oxide, barium sulfate, calcium carbonate, magnesiumoxide, tungsten powder, and molybdenum powder. The amount of the fillerto be blended in the rubber composition is preferably 2 parts or more,more preferably 3 parts or more, and preferably 50 parts or less, morepreferably 35 parts or less based on 100 parts of the base rubber bymass. If the amount of the filler to be blended is less than 2 parts bymass, it becomes difficult to adjust the weight, while if it is morethan 50 parts by mass, the weight ratio of the rubber component becomessmall and the resilience tends to be lowered.

As the core rubber composition, an organic sulfur compound, anantioxidant or a peptizing agent may be blended appropriately inaddition to the base rubber, the crosslinking initiator, theco-crosslinking agent and the filler.

As the organic sulfur compound, a diphenyl disulfide or a derivativethereof may be preferably used. Examples of the diphenyl disulfide orthe derivative thereof include diphenyl disulfide; a mono-substituteddiphenyl disulfide such as bis(4-chlorophenyl)disulfide,bis(3-chlorophenyl)disulfide, bis(4-bromophenyl)disulfide,bis(3-bromophenyl)disulfide, bis(4-fluorophenyl)disulfide,bis(4-iodophenyl)disulfide and bis(4-cyanophenyl)disulfide; adi-substituted diphenyl disulfide such asbis(3,5-dichlorophenyl)disulfide, bis(2,6-dichlorophenyl)disulfide,bis(2,5-dibromophenyl)disulfide, bis(3,5-dibromophenyl)disulfide,bis(2-chloro-5-bromophenyl)disulfide, andbis(2-cyano-5-bromophenyl)disulfide; a tri-substituted diphenyldisulfide such as bis(2,4,6-trichlorophenyl)disulfide, andbis(2-cyano-4-chloro-6-bromophenyl)disulfide; a tetra-substituteddiphenyl disulfide such as bis(2,3,5,6-tetra chlorophenyl)disulfide; apenta-substituted diphenyl disulfide such asbis(2,3,4,5,6-pentachlorophenyl)disulfide andbis(2,3,4,5,6-pentabromophenyl)disulfide. These diphenyl disulfides orthe derivative thereof can enhance resilience by having some influenceon the state of vulcanization of vulcanized rubber. Among them, diphenyldisulfide and bis(pentabromophenyl)disulfide are preferably used, sincea golf ball having particularly high resilience can be obtained. Theamount of the diphenyl disulfide or the derivative thereof to be blendedis preferably 0.1 part by mass or more, more preferably 0.3 part by massor more, and preferably 5.0 parts by mass or less, more preferably 3.0parts by mass or less relative to 100 parts by mass of the base rubber.

The amount of the antioxidant to be blended is preferably 0.1 part ormore and is preferably 1 part or less based on 100 parts of the baserubber by mass. Further, the amount of the peptizing agent is preferably0.1 part or more and is preferably 5 parts or less based on 100 parts ofthe base rubber by mass.

The conditions for press-molding the rubber composition should bedetermined depending on the rubber composition. The press-molding ispreferably carried out for 10 to 60 minutes at the temperature of 130 to200° C. Alternatively, the press-molding is preferably carried out in atwo-step heating, for example, for 20 to 40 minutes at the temperatureof 130 to 150° C., and continuously for 5 to 15 minutes at thetemperature of 160 to 180° C.

The core used in the golf ball of the present invention preferably has adiameter of 39 mm or larger, more preferably 39.5 mm or larger, and evenmore preferably 40.8 mm or larger, and preferably has a diameter of 42.2mm or smaller, more preferably 42 mm or smaller, and even morepreferably 41.8 mm or smaller. If the diameter of the core is smallerthan the above lower limit, the cover becomes so thick that theresulting golf ball would have reduced resilience. On the other hand, ifthe diameter of the core is larger than the above upper limit, the coverbecomes so thin that it is difficult to mold a cover.

In the case that the core has a diameter of from 39 mm to 42.2 mm, thecompression deformation amount (deformation amount along the shrinkagedirection) of the core when applying a load from 98 N as an initial loadto 1275 N as a final load is preferably 2.50 mm or more, more preferably2.60 mm or more, and is preferably 3.20 mm or less, and more preferably3.10 mm or less. If the above deformation amount is less than 2.50 mm,the core becomes too hard, resulting in worsening the shot feeling,while if the above deformation amount is larger than 3.20 mm, therepulsion property may be lowered.

In a preferable embodiment, the core has a hardness difference betweenthe center and the surface. The difference between the surface hardnessand the center hardness is preferably 10 or more, more preferably 12 ormore, and is preferably 40 or less, more preferably 35 or less, and evenmore preferably 30 or less in JIS-C hardness. If the hardness differenceis more than 40, the durability may be lowered, while if the hardnessdifference is less than 10, the shot feeling may be hard because of alarge impact. The surface hardness of the core is preferably 65 or more,more preferably 70 or more, even more preferably 72 or more, and ispreferably 100 or less in JIS-C hardness. If the surface hardness of thecore is less than 65 in JIS-C hardness, the core is so soft and therepulsion property may be lowered, resulting in shortening the flightdistance. On the other hand, if the surface hardness of the core is morethan 100, the core is so hard and the shot feeling may be lowered. Thecenter hardness of the core is preferably 45 or more, more preferably 50or more, and is preferably 70 or less, and more preferably 65 or less inJIS-C hardness. If the center hardness of the core is less than 45, thecore is so soft and the durability may be lowered, while if the centerhardness of the core is more than 70, the core is so hard and the shotfeeling may be worsened. The hardness difference of the core can beformed by properly selecting the heat molding conditions of the core.

In the case that the golf ball of the present invention is a three-piecegolf ball or a multi-piece golf ball, examples of the material for theintermediate layer are a thermoplastic polyamide elastomer having acommercial name of “Pebax (registered trademark) (e.g. Pebax 2533)”available from Arkema; a thermoplastic polyester elastomer having acommercial name of “Hytrel (registered trademark) (e.g. Hytrel 3548,Hytrel 4047)” available from Du Pont-Toray Co., Ltd.; a thermoplasticpolyurethane elastomer having a commercial name of “Elastollan(registered trademark) (e.g. Elastollan XNY97A)” available from BASFJapan Co., a thermoplastic polystyrene elastomer having a commercialname of “Rabalon (registered trademark) (e.g. Rabalon SR04, RabalonT3339C, Rabalon T3221C)” available from Mitsubishi Chemical Corporation,in addition to the cured product of the rubber composition or theconventional ionomer resin. The intermediate layer may further contain agravity adjusting agent such as barium sulfate, tungsten or the like, anantioxidant, and a pigment or the like.

In the case of using the intermediate layer composition containing arubber composition as a main component (50 mass % or more), theintermediate layer preferably has a thickness of 1.2 mm or more, morepreferably 1.8 mm or more, even more preferably 2.4 mm or more, andpreferably has a thickness of 6.0 mm or less, more preferably 5.2 mm orless, even more preferably 4.4 mm or less.

In the case of using the intermediate layer composition containing theresin composition as a main component (50 mass % or more), theintermediate layer preferably has a thickness of 0.3 mm or more, morepreferably 0.4 mm or more, even more preferably 0.5 mm or more, andpreferably has a thickness of 2.5 mm or less, more preferably 2.4 mm orless, even more preferably 2.3 mm or less. If the thickness of theintermediate layer is more than 2.5 mm, the resilience performance ofthe obtained golf ball may be lowered, while if the thickness of theintermediate layer is less than 0.3 mm, it may be difficult to suppressthe excessive spin rate on the driver shot.

The intermediate layer of the golf ball of the present inventionpreferably has a slab hardness of 50 or larger, more preferably 52 orlarger, and even more preferably 54 or larger, and preferably has a slabhardness of 75 or smaller, more preferably 73 or smaller, and even morepreferably 71 or smaller in Shore D hardness. The intermediate layerhaving the slab hardness of 50 or more in shore D hardness makes thecore have the higher degree of “hard outer and soft inner” structure,thereby providing a high launch angle and a less amount of spin andhence achieving a large flight distance of the gold ball. On the otherhand, the intermediate layer having the slab hardness of 75 or less inshore D hardness provides an excellent shot feeling as well as improvesthe spin performance of the golf ball, thereby improving controllabilityof the golf ball. Herein, the slab hardness of the intermediate layer isthe measured hardness of the intermediate layer composition in the formof a sheet, and is measured by a later-described measuring method. Theslab hardness of the intermediate layer can be adjusted, for example, byappropriately selecting a combination of the above resin component andthe rubber material and the amount of additives.

An embodiment for molding the intermediate layer is not particularlylimited, and includes an embodiment which comprises injection moldingthe intermediate layer composition directly onto the center, or anembodiment which comprises molding the intermediate layer compositioninto a half hollow-shell, covering the center with the two hollow-shellsand subjecting the center with the two hollow shells to thecompression-molding at the temperature of 130° to 170° for 1 to 5minutes.

When preparing a wound golf ball in the present invention, a wound coremay be used as the core. In that case, for example, a wound corecomprising a center formed by curing the above rubber composition forthe core and a rubber thread layer which is formed by winding a rubberthread around the center in an elongated state can be used. In thepresent invention, the rubber thread, which is conventionally used forwinding around the center, can be adopted for winding around the center.The rubber thread, for example, is obtained by vulcanizing a rubbercomposition including a natural rubber, or a mixture of a natural rubberand a synthetic polyisoprene, a sulfur, a vulcanization auxiliary agent,a vulcanization accelerator, and an antioxidant. The rubber thread iswound around the center in elongation of about 10 times length to formthe wound core.

The golf ball of the present invention is not particularly limited on astructure thereof as long as the golf ball includes a core and a cover.Examples of the golf ball of the present invention include a two-piecegolf ball including a core, and a cover covering the core; a three-piecegolf ball including a core consisting of a center and an intermediatelayer covering the center, and a cover covering the core; a multi-piecegolf ball including a core consisting of a center and a multi-piece ormulti-layer of intermediate layers covering the center, and a covercovering the core; and a wound golf ball including a wound core, and acover covering the wound core.

EXAMPLES

The following examples illustrate the present invention, however theseexamples are intended to illustrate the invention and are not to beconstrued to limit the scope of the present invention. Many variationsand modifications of such examples will exist without departing from thescope of the inventions. Such variations and modifications are intendedto be within the scope of the invention.

[Evaluation Methods] (1) Abrasion-Resistance

A commercially available sand wedge (available from SRI sports limited,S shaft) was installed on a swing robot available from GolfLaboratories, Inc., and two points of a ball were both hit once at ahead speed of 36 m/sec to observe the portions which were hit. Each hitportion was evaluated and ranked into eight levels based on thefollowing criteria, and an average rank score for the two points wascalculated. A smaller score indicates higher abrasion-resistance.

0 point: No hitting marks were observed.

1 point: Dot-like peeling (a maximum size is smaller than 3 mm) wasobserved.

2 point: Dot-like peeling (a maximum size is 3 mm or larger) wasobserved.

3 point: Line-like peeling (a maximum size is 5 mm or larger) wasobserved.

4 point: Clear line-like peeling (a maximum size is 5 mm or larger) wasobserved.

5 point: Deep and wide line-like peeling (a maximum size is 5 mm orlarger) was observed.

6 point: Deep and wide peeling which was almost a plane was observed.

7 point: A part of the cover was scraped away as a plane.

(2) Spin Rate

An approach wedge (SRIXON I-302 available from SR1Sports Limited) wasinstalled on a swing robot available from Golf Laboratories, Inc. A golfball was hit at a head speed of 21 m/sec., and a sequence of photographsof the hit golf ball were taken for measuring the spin rate (rpm). Themeasurement was performed ten times for each golf ball, and the averagevalue is regarded as the spin rate(rpm).

(3) Slab Hardness (Shore D Hardness)

Sheets having a thickness of about 2 mm were prepared from the covercomposition or the intermediate layer composition by hot press moldingand preserved at the temperature of 23° C. for two weeks. Three or moreof the sheets were stacked on one another to avoid being affected by themeasuring substrate on which the sheets were placed, and the stack wassubjected to the measurement using a P1 type auto hardness testerprovided with the Shore D type spring hardness tester prescribed byASTM-D2240, available from KOUBUNSHI KEIKI CO., LTD to obtain therespective slab hardness of the cover composition or the intermediatelayer composition.

(4) Core Hardness (JIS-C)

The hardness measured at a surface part of a spherical core using aJIS-C type spring hardness tester specified by JIS K6301, was determinedas the surface hardness of the spherical core, and the JIS-C hardnessobtained by cutting a spherical core into halves and measuring at thecenter of the cut surface was determined as the center hardness of thespherical core.

[Production of the Golf Ball] (1) Preparation of the Center

The center rubber compositions having formulation shown in Table 1 werekneaded and pressed in upper and lower molds, each having ahemispherical cavity, at a temperature of 170° C. for 15 minutes toobtain the center with a spherical shape.

TABLE 1 Center composition A B Polybutadiene rubber 100 100 Zincacrylate 35 38 Zinc oxide 5 5 Diphenyl disulfide 0.5 0.5 Dicumylperoxide 1 1 Notes on table 1: Parts by mass Polybutadiene rubber: BR730(high cis-polybutadiene) manufactured by JSR Corporation Zinc acrylate:ZNDA-90S manufactured by NIHON JYORYU KOGYO Co,. LTD. Zinc oxide: GinreiR manufactured by Toho-Zinc Co. Dicumyl peroxide: Percumyl Dmanufactured by NOF Corporation Diphenyl disulfide: manufactured bySumitomo Seika Chemicals Company Limited

(2) Preparation of Core Core Nos. 1 to No. 4, No. 6 to No. 8

Next, the materials for the intermediate layer shown in Table 2 weremixed by a twin-screw kneading extruder to prepare an intermediate layercomposition in the form of pellet. Extrusion was performed in thefollowing conditions: screw diameter=45 mm; screw revolutions=200 rpm;and screw L/D=35. The mixtures were heated to a temperature ranging from150° C. to 230° C. at a die position of the extruder. The obtainedintermediate layer composition was injection molded on the center whichhad been obtained as described above, to prepare a core consisting ofthe center and the intermediate layer covering the center.

Core No. 5

The intermediate layer composition was first kneaded and the upper diefor molding a center in the state that the center was set therein and alower die for molding a core were clamped in a manner that a necessaryamount of the intermediate layer composition was brought into contactwith a half of the surface of the center and heat pressing was carriedout to produce an intermediate core molded product having anintermediate layer formed on a half of the surface of the center. Next,the lower die for molding the core in the state that the intermediatelayer of the intermediate core molded product was housed and an upperdie for molding a core were clamped in a manner that a necessary amountof the intermediate layer composition was brought into contact with theother half of the surface of the center and heat pressing was carriedout to produce a core having an intermediate layer on the other half ofthe surface of the center.

Core No. 9

The center was used as the core.

TABLE 2 Core No. 1 2 3 4 5 6 7 8 9 Center Center composition A A A A A AA A B Center diameter (mm) 38.5 38.5 38.5 39.7 36.7 38.9 37.5 35.5 41.7Intermediate Intermediate layer a b c d e f g h — layer compositionHimilan 1605 50 40 — 50 — 50 50 50 — Himilan AM7329 50 35 — 50 — 50 5050 — Rabalon T3221C — 25 — — — — — — — Surlyn 8140 — — 50 — — — — — —Surlyn 9120 — — 50 — — — — — — Polybutadiene — — — — 100 — — — — Zincacrylate — — — — 40 — — — — Zinc oxide — — — — 5 — — — — Diphenyldisulfide — — — — 0.5 — — — — Dicumyl peroxide — — — — 1 — — — — Slabhardness 64 50 69 64 60 64 64 64 — (Shore D) Thickness (mm) 1.6 1.6 1.61 2.5 1.6 1.6 1.6 — Core Diameter (mm) 41.7 41.7 41.7 41.7 41.7 42.140.7 38.7 41.7 Property Surface hardness 98 80 99 98 88 98 98 98 86(JIS-C) Center hardness 65 65 65 65 65 65 65 65 67 (JIS-C) Hardnessdifference 33 15 34 33 23 33 33 33 19 (JIS-C) Compression deformation2.55 2.75 2.45 2.7 2.35 2.55 2.55 2.5 2.6 amount (mm) Formulation: partsby mass Notes on table 2: Himilan 1605: sodium ion neutralizedethylene-methacrylic acid copolymerized ionomer resin manufactured byMITSUI-DUPONT POLYCHEMICAL CO., LTD. Himilan AM7329: zinc ionneutralized ethylene-methacrylic acid copolymerized ionomer resinmanufactured by MITSUI-DUPONT POLYCHEMICAL CO., LTD. Rabalon T3221C:Thermoplastic polystyrene elastomer available from Mitsubishi ChemicalCorporation. SURLYN 8140: a sodium ion neutralized ethylene-methacrylicacid copolymer ionomer resin available from E.I. du Pont de Nemours andCompany. SURLYN 9120: a zinc ion neutralized ethylene-methacrylic acidcopolymer ionomer resin available from E.I. du Pont de Nemours andCompany. Polybutadiene rubber: BR730 (high cis-polybutadiene)manufactured by JSR Corporation Zinc acrylate: ZNDA-90S manufactured byNIHON JYORYU KOGYO Co,. LTD. Zinc oxide: Ginrei R manufactured byToho-Zinc Co. Dicumyl peroxide: Percumyl D manufactured by NOFCorporation Diphenyl disulfide: manufactured by Sumitomo Seika ChemicalsCompany Limited

(3) Preparation of Cis-Trans Mixture

The cis-trans mixtures were prepared by mixing 1,4-cyclohexanedimethanol (cis/trans mass ratio=74/26) and 1,4-cyclohexane dimethanol(cis/trans mass ratio=0/100), available from TOKYO CHEMICAL INDUSTRYCo., Ltd, based on the mixing ratio shown in Table 3 and 4. The mixingratio of cis-trans mixture can be measured using gas chromatographyequipment under the following conditions.

(Measuring Conditions of Gas Chromatography)

Column: DB-1 (available from Shimadzu Corporation), 30 m×0.25 mm×0.25μm.Temperature: Kept at 150° C. for 2 minutes, then raised to 250° C. atthe rate of 5° C./min, then raised to 300° C. at the rate of 10° C./min,and kept at 300° C. for 3 minutes.Injection temperature: 280° C.Detector temperature: 280° C.Carrier gas: helium (at flow rate of 2 ml/min.)

[Synthesis of the Polyurethane]

To have the compositions as shown in Table 3 and 4, first, PTMG2000heated at the temperature of 80° C. was added to MDI heated at thetemperature of 80° C. Then, dibutyl tin dilaurate (dibutyl tin dilaurateavailable from Aldrich, Inc.) of 0.005 mass % of the total amount of theraw materials (MDI, PTMG2000, and Chain extender) was added thereto.Then, the mixture was stirred at the temperature of 80° C. for 2 hoursunder a nitrogen gas flow. Under a nitrogen gas flow, the cis-transmixture heated at the temperature of 80° C. was added as a chainextender to the mixture, and the mixture was stirred at the temperatureof 80° C. for 1 minute. Then, the reaction liquid was cooled, anddegassed under the reduced pressure for 1 minute at the roomtemperature. After the degassing, the reaction liquid was spread in acontainer, kept at the temperature of 110° C. for 6 hours under anitrogen gas atmosphere to carry out a chain extending reaction, therebyobtaining polyurethanes.

TABLE 3 Golf ball No. 1 2 3 4 5 6 7 8 9 Core No. 1 1 1 1 1 1 1 1 1Intermediate layer Shore D 64 64 64 64 64 64 64 64 64 hardnessIntermediate layer mm 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6 thickness CoreDiameter mm 41.7 41.7 41.7 41.7 41.7 41.7 41.7 41.7 41.7 CoverPolyurethane Parts by mass 100 composition Constituting M.W. Molar ratiocomponent PTMG2000 2000  1 1 1 1 1 1 1 1 1 MDI 250 4 4 4 4 4 4 4 4 4CHDM 144 3 3 3 3 3 3 3 3 — BD  90 — — — — — — — — 3 Cis/Trans ratio massratio 70/30 60/40 50/50 40/60 30/70 20/80 10/90 0/100 0 Slab hardness ofShore D 38 38 39 39 40 42 44 48 36 polyurethane Titanium oxide Parts bymass 4 Cover thickness mm 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Slabhardness Shore D 39 39 40 40 41 43 45 49 37 Property Abrasion-resistance1 1 1 1 1 2 3 6 6 Spin performance (rpm) 6400 6800 6900 7000 7000 70007000 7000 7000 Formulation of polyurethane: molar ratio Formulation ofcover composition: parts by mass M.W.: molecular weight

TABLE 4 Golf ball No. 10 11 12 13 14 15 16 17 18 19 Core No. 1 1 6 7 8 92 3 4 5 Intermediate layer Shore D 64 64 64 64 64 — 50 69 64 60 hardnessIntermediate layer mm 1.6 1.6 1.6 1.6 1.6 — 1.6 1.6 1 2.5 thickness CoreDiameter mm 41.7 41.7 42.1 40.7 38.7 41.7 41.7 41.7 41.7 41.7 CoverPolyurethane Parts by mass 100 composition Constituting M.W. Molar ratiocomponent PTMG2000 2000  1 1 1 1 1 1 1 1 1 1 MDI 250 2.2 5.5 4 4 4 4 4 44 4 CHDM 144 1.2 4.5 3 3 3 3 3 3 3 3 BD  90 — — — — — — — — — —Cis/Trans ratio mass ratio 30/70 30/70 30/70 30/70 30/70 30/70 30/7030/70 30/70 30/70 Slab hardness of Shore D 19 49 40 40 40 40 40 40 40 40polyurethane Titanium oxide Parts by mass 4 Cover thickness mm 0.5 0.50.3 1.0 2.0 0.5 0.5 0.5 0.5 0.5 Slab hardness Shore D 20 50 41 41 41 4141 41 41 41 Property Abrasion-resistance 1 1 1 0.5 0.5 0.5 0.5 1 1 1Spin performance (rpm) 8000 5500 6900 7300 7400 7500 7300 6900 7400 7300Formulation of polyurethane: molar ratio, Formulation of covercomposition: parts by mass M.W.: molecular weight

Materials in Tables 3 and 4:

MDI: Sumidur 44S available from Sumika Bayer Urethane Co., Ltd.PTMG2000: Polytetramethylene ether glycol, PTMG-2000SN (Number averagemolecular weight 2000) available from HODOGAYA CHEMICAL Co., Ltd.CHDM: 1,4-cyclohexane dimethanol available from TOKYO CHEMICAL INDUSTRYCo., LtdBD: 1,4-butanediol available from WAKO Pure Chemicals, Industries, Ltd.

(5) Formulating of Cover Compositions

The cover materials shown in Tables 3 and 4 were mixed by a twin-screwkneading extruder to prepare cover compositions in the form of pellet.Extrusion was performed in the following conditions: screw diameter=45mm; screw revolutions=200 rpm; and screw L/D=35. The mixtures wereheated to a temperature ranging from 150° C. to 230° C. at a dieposition of the extruder.

(6) Molding of Half Shells

Compression molding of half shells were performed by, charging onepellet of the cover composition obtained as described above into each ofdepressed parts of lower molds for molding half shells, and applyingpressure to mold half shells. Compression molding was performed at atemperature of 180° C. for 5 minutes under a molding pressure of 2.94MPa.

(7) Molding of the Cover

The core obtained in (2) was covered with the two half shells obtainedin (6) in a concentric manner, and the cover was molded by compressionmolding. Compression molding was performed at a temperature of 150° C.for 2 minutes under a molding pressure of 9.8 MPa. The surface of theobtained golf ball body was subjected to a sandblast treatment, andmarking, and then clear paint was applied thereto and dried in an ovenat a temperature of 40° C. to obtain a golf ball having a diameter of42.7 mm and a weight of 45.3 g. Abrasion-resistance and spin performanceof the obtained golf ball were evaluated, and results thereof are shownin Tables 3 and 4.

Golf balls No. 1 to 7 are the cases where the cover containspolyurethane as a resin component, wherein the polyurethane has, as aconstituting component, a polyisocyanate component, a high-molecularweight polyol component, and a mixture of cis-1,4-cyclohexane dimethanoland trans-1,4-cyclohexane dimethanol as a chain extender. The resultsindicated that the abrasion-resistance is improved compared with thegolf ball No. 8 using only trans-1,4-cyclo-hexane dimethanol and thegolf ball No. 9 using 1,4-butanediol as a chain extender. Especially, ifthe mixing ratio (cis/trans) of cis-structure to trans-structure fallswithin the range from 60/40 to 30/70, both of the abrasion-resistanceand the spin performance were achieved at the higher level. Thecomparison of the golf ball No. 10 and the golf ball No. 11 indicatedthat the spin performance was improved by lowering the slab hardness ofthe cover. The comparison of the golf ball No. 5, and Nos. 12 to 14indicated that the spin performance and the abrasion-resistance wereimproved by using the thicker cover.

The present invention can be suitably applied to the golf ball having acover, and especially suitable for the improvement of theabrasion-resistance and the spin performance of the cover using thepolyurethane as a resin component. This application is based on JapanesePatent application No. 2009-154726 filed on Jun. 30, 2009, the contentsof which are hereby incorporated by reference.

1. A golf ball comprising: a core; and a cover covering the core andcontaining polyurethane as a resin component, wherein the polyurethanehas, as a constituting component, a polyisocyanate component, ahigh-molecular weight polyol component, and a mixture ofcis-1,4-cyclohexane dimethanol and trans-1,4-cyclohexane dimethanol as achain extender.
 2. The golf ball according to claim 1, wherein a mixingratio of cis-1,4-cyclohexane dimethanol to trans-1,4-cyclohexanedimethanol falls within a range from 10/90 to 70/30 in a mass ratio. 3.The golf ball according to claim 1, wherein a mixing ratio ofcis-1,4-cyclohexane dimethanol to trans-1,4-cyclohexane dimethanol fallswithin a range from 30/70 to 40/60 in a mass ratio.
 4. The golf ballaccording to claim 1, wherein the polyurethane contains diphenylmethanediisocyanate as the polyisocyanate component.
 5. The golf ball accordingto claim 1, wherein the polyurethane containspolyoxytetramethyleneglycol as the high-molecular weight polyolcomponent.
 6. The golf ball according to claim 1, wherein the cover hasa hardness ranging from 20 to 50 in shore D hardness.
 7. The golf ballaccording to claim 1, wherein the cover has a thickness ranging from 0.3mm to 2.5 mm.
 8. The golf ball according to claim 1, wherein the core isa multi-layered core having a center and at least one intermediate layercovering the center.
 9. The golf ball according to claim 8, wherein theintermediate layer has a hardness ranging from 50 to 75 in Shore Dhardness.
 10. The golf ball according to claim 8, wherein theintermediate layer has a thickness ranging from 0.3 mm to 6.0 mm. 11.The golf ball according to claim 1, wherein the core has a hardnessdifference between a surface hardness and a center hardness ranging from10 to 40 in JIS-C hardness.
 12. The golf ball according to claim 1,wherein the high-molecular weight polyol has a number average molecularweight of more than 400 and 10,000 or less.
 13. The golf ball accordingto claim 1, wherein the high-molecular weight polyol has a hydroxylvalue of 500 mgKOH/g or less.
 14. The golf ball according to claim 1,wherein the polyurethane has a hardness ranging from 15 to 50 in Shore Dhardness.
 15. The golf ball according to claim 1, wherein thepolyurethane is obtained by a reaction of the polyisocyanate component,the high-molecular weight polyol and the chain extender in a molar ratio(NCO/OH) of an isocyanate group (NCO) contained in the polyisocyanatecomponent to a hydroxyl group (OH) contained in the high-molecularweight polyol component ranging from 1 to
 10. 16. The golf ballaccording to claim 1, wherein the polyurethane is obtained by a reactionof the polyisocyanate component, the high-molecular weight polyol andthe chain extender in a molar ratio (NCO/OH) of an isocyanate group(NCO) contained in an isocyanate group terminated urethane prepolymer toa hydroxyl group (OH) contained in the chain extender ranging from 0.9to 1.1.
 17. A golf ball comprising: a core; and a cover covering thecore and containing polyurethane as a resin component, wherein thepolyurethane has, as a constituting component, a polyisocyanatecomponent, a high-molecular weight polyol component, and a mixture ofcis-1,4-cyclohexane dimethanol and trans-1,4-cyclohexane dimethanol as achain extender, wherein a mass ratio of cis-1,4-cyclohexane dimethanolto trans-1,4-cyclohexane dimethanol falls within a range from 10/90 to70/30.
 18. The golf ball according to claim 17, wherein the polyurethanecontains diphenylmethane diisocyanate as the polyisocyanate componentand polyoxytetramethyleneglycol as the high-molecular weight polyolcomponent, and the polyurethane has a hardness ranging from 15 to 50 inShore D hardness.
 19. The golf ball according to claim 18, wherein thecore is a multi-layered core having a center and at least oneintermediate layer covering the center, the intermediate layer has ahardness ranging from 50 to 75 in Shore D hardness, and the intermediatelayer has a thickness ranging from 0.3 mm to 6.0 mm.
 20. The golf ballaccording to claim 19, wherein a mixing ratio of cis-1,4-cyclohexanedimethanol to trans-1,4-cyclohexane dimethanol falls within a range from30/70 to 40/60 in a mass ratio.